1. Field of the Invention
This invention relates generally to the field of computer accessories, and in particular to devices for the scanning of images for storage and processing by computers in the digital domain.
2. Description of the Prior Art
In informal parlance, scanning refers to the use of an optical machine to convert an image into a machine-readable file for manipulation, use, or printing by computers, so that term will be used for simplicity and clarity hereafter.
The design of a so called `flat-bed` scanner looks and operates much like a photocopy machine in reverse: it has a glass window where the original is placed for scanning; the original is usually not moved during the scanning process; and the optical sensing part of the scanner itself is not physically manipulated by the operator during normal operation. All relative motion between the original and the scanning apparatus in a flat-bed scanner is done by the scanner itself. Because of the level of mechanical complexity involved with this design most flat bed scanners are relatively expensive. More inexpensive scanning is generally accomplished by using hand-held scanners.
Hand-held scanners have no internal mechanism for controlling the relation of the scanner to the source object. This relation is controlled by the user when he passes the scanner over the source document while holding the scanning button on. The digital quality of images retrieved by using hand-held scanners is actually quite high, but there is no easy method to precisely orient the scanner to the source document squarely, in relation to the natural X-Y axis of that document. Results of hand scanning are mostly unsatisfactory because the human hand can not pull the scanner in a perfectly vertical pattern from the top of a page to the bottom. Current hand scanners are capable of resolutions beginning at about 300 lines per inch; even the most steadfast human would find it difficult if not impossible not to stray a few hundredths of an inch to the left or right moving a scanner down a page. When the scanner is not moved in a square vertical fashion the resultant output has the entire scanned image slightly skewed horizontally along the page. This means perfectly vertical lines in the original image are incorrectly slanted. Though attempts have been made to correct skewed scans such as these with computer programs for straightening out the lines, there is no substitute for having a straight scan in the first place because there is always information loss.
Another problem with free hand use of hand scanners involves securely holding the original to be scanned. Even if the scanner is pulled in a fairly straight motion across the source document any movement of the original during the scanning process also results in skewed output.
Additionally, results are not repeatable with hand-held scanners because each scanning attempt yields a different relation between the source document and the scanner itself. As a result, there can be no reiterative refinement of subsequent scans. This can probably be best understood by contrasting with a flat bed scanner where the relation of the original to the scanning mechanism stays constant until the original is moved. This means the flat bed design can make a first pass to `preview` what the final scan would look like. This kind of feature can not be used with hand scanners because the relation between the original image and the scanner is not constant among scanning attempts.
Current hand scanning systems suffer from a number of disadvantages:
(a) No capability for starting the scanner in the same part of the original image with each scan in a series.
(b) No provision for holding the original image securely.
(c) No provision for holding a thick original image, as in a book.
(d) No capability for restricting the motion of the scanner over the source image to follow a precise vertical path.
(e) No apparatus for physically orienting the scanner itself in a precise relation to other objects or images.
(f) No provision for aligning the relation of the scanner to the natural vertical orientation of the original image.
(g) No system of calibration for repeatedly relating the scanner to the original image.